This invention relates generally to fluid controls and more particularly relates to a chemically inert fluid control module that may be connected in-line within a chemically corrosive fluid flow circuit that delivers fluids in either a liquid or gaseous state. The fluid control module of the present invention may be utilized to control the flow, pressure or volume of fluid flowing through the fluid flow circuit and is capable of automatically adjusting or xe2x80x9ccalibratingxe2x80x9d the module to compensate for changes in atmospheric pressure or drift in the pressure sensors of the fluid control module.
Caustic fluids are frequently used during ultra pure processing of sensitive materials. The susceptibility to contamination of the sensitive materials during the manufacturing process is a significant problem faced by manufacturers. Various manufacturing systems have been designed to reduce the contamination of the sensitive materials by foreign particles and vapors generated during the manufacturing process. The processing of the sensitive materials often involves direct contact with caustic fluids. Hence, it is critical that the caustic fluids are delivered to the processing site in an uncontaminated state and without foreign particulate. Various components of the processing equipment are commonly designed to reduce the amount of particulate generated and to isolate the processing chemicals from contaminating influences.
The processing equipment typically includes liquid transporting systems that carry the caustic chemicals from supply tanks through pumping and regulating stations and through the processing equipment itself. The liquid chemical transport systems, which includes pipes, tubing, monitoring devices, sensing devices, valves, fittings and related devices, are frequently made of plastics resistant to the deteriorating effects of the caustic chemicals. Metals, which are conventionally used in such monitoring devices, cannot reliably stand up to the corrosive environment for long periods of time. Hence, the monitoring and sensing devices must incorporate substitute materials or remain isolated from the caustic fluids.
The processing equipment commonly used in semiconductor manufacturing has one or more monitoring, valving, and sensing devices. These devices are typically connected in a closed loop feedback relationship and are used in monitoring and controlling the equipment. These monitoring and sensing devices must also be designed to eliminate any contamination that might be introduced.
In order to control the flow or pressure within the liquid transporting system, the transporting equipment may utilize information obtained from each of the monitoring, valving and sensing devices. The accuracy of the information obtained from each of the devices may be affected by thermal changes within the system. Further, the inaccuracy of one device may compound the inaccuracy of one of the other devices that depends upon information from the one device. Further, frequent independent calibration may be required to maintain the accuracy of each individual device, however, independent calibration of the devices may prove difficult and time consuming.
Hence, there is a need for a non-contaminating fluid control module which may be positioned in-line within a fluid flow circuit carrying corrosive materials, wherein the module is capable of determining the rate of flow based upon a pressure differential measurement taken in the fluid flow circuit, and wherein the determination of the rate of flow is not adversely affected by thermal changes within the fluid flow circuit, and wherein calibration of the pressure sensors of the fluid control module does not require ancillary or independent calibration of the valve. A need also exists for a fluid control module that avoids the introduction of particulate, unwanted ions, or vapors into the flow circuit. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.
The present invention provides for a fluid control module that may be coupled in-line to a fluid flow circuit that transports corrosive fluids, where the fluid control module may determine pressure and flow rates and control the pressure, flow or volume within the fluid flow circuit. The rate of flow may be determined from a differential pressure measurement taken within the flow circuit. The fluid control module compensates for changes of temperature within the fluid flow circuit and provides a zeroing feature which compensates for differences in pressure when the fluid is at rest and negates the affects of the valve upon the system. In the preferred embodiment, the components of the fluid control module include a housing having a chemically inert fluid conduit, an adjustable control valve coupled to the conduit, pressure sensors coupled to the conduit, and a constriction disposed within the conduit having a reduced cross-sectional area to thereby restrict flow of fluid within the conduit and allow for reliable flow measurement. The chemically inert housing encloses the control valve and the pressure sensors.
When two pressure sensors are provided, the constriction is positioned between the two pressure sensors within the fluid flow conduit. As described in greater detail below, the fluid control module of the present invention having two pressure sensors provides for bi-directional fluid flow and may be coupled in line to adjacent ancillary equipment. In an alternate preferred embodiment, the fluid control module includes only one pressure sensor, wherein the constriction within the fluid conduit must be positioned downstream of the pressure sensor and valve. Also, the fluid control module having a single pressure sensor must be spaced apart a predetermined distance from ancillary equipment connected in line to the fluid flow circuit.
The drive or actuation of the control valve may be driven either mechanically, electrically or pneumatically by a driver having a known suitable construction and the valving components within the control valve may take on any of several suitable known configurations, including without limitation a poppet, diaphragm, redundant diaphragm, weir valve and/or pinch valve, wherein the components in direct contact with the fluid of the fluid flow circuit are constructed from chemically inert materials.
A controller or integrated circuit may be electrically coupled to the control valve and pressure sensor or sensors. The controller may produce a signal proportional to a fluid flow rate within the fluid conduit and/or a signal proportional to a pressure within the fluid conduit. The controller may control the pressure, rate of flow, or volume such that a desired set point is maintained. The set point may be defined by the user or automatically determined by the controller (for example, during a macro adjustment of the control valve). Further, the controller may adjust the fluid flow rate signal or pressure signal dependant upon changes in atmospheric or fluid pressure. Also, the controller may include a means for macro and micro adjustment of the control valve in response to changes in internal fluid or atmospheric pressure and may re-zero the pressure sensors when flow within the fluid flow circuit stops.
The housing that encloses the control valve and pressure sensors includes a bore extending therethrough, which forms a passage or conduit through which fluids flow, when the housing is connected in-line in a fluid flow circuit. Aligned and sealably connected to the opposed open ends of the bore are pressure fittings. The pressure fittings are constructed from a chemically inert material and are readily available and known to those skilled in the art.
In an embodiment of the present invention the housing has two pressure transducer receiving cavities extending from an external surface thereof, wherein each such cavity communicates independently with the bore. An isolation member may prevent the fluid flow from contacting the pressure transducer receiving cavities. The isolation members may be molded integral with the housing or may be removable. The bore tapers to a constricting region located between the two cavities. The restricted region results in a pressure drop within the bore across points adjacent the two cavities. This change in pressure may be detected by pressure sensor transducers placed within each of the two cavities. The rate of flow may be determined from the drop in pressure. The determination of the rate of flow using the two pressure sensors is described below in greater detail.
A hybrid or fully integrated electronic circuit disposed in the housing is operatively coupled to both pressure sensor transducers and the control valve. The electronic circuit develops a signal that is a measure of the rate of flow within the flow circuit from information sensed by the pressure sensors. Further, the electronic circuit may develop a signal corresponding to one or the other of the downstream or upstream static pressures within the fluid flow circuit, such that the orientation of the flow meter within the flow circuit is interchangeable and the direction of flow may be indicated by comparing the sensed pressure from each pressure sensor. When sensing the static pressures of gases flowing through the flow circuit, a correction may be made to the sensed pressures to correct for non-linearity and flow rates as a result of gas density and compressibility differences and effects.
This electronic circuit may also be used in combination with temperature sensitive components to adjust the pressure measurement associated with each cavity based upon temperature changes within the flow circuit. Further, the electronic circuit or controller may allow for zeroing of the pressure sensors and valve control. The electronic circuit is coupled by electrical leads to an electrical connector and power may be transmitted to the electronic circuit through the electrical leads connected to an external power supply. Further, an analog output such as a standard 4-20 milliamps signal, voltage output, or digital protocol proportional to the calculated rate of flow may be transmitted through additional electrical leads to a display or external controller.
The isolation membrane, pressure sensor, sealing members, spacer ring and hold down ring may be contained within each cavity of the housing. These components and variations thereof are described in greater detail in U.S. Pat. Nos. 5,869,766 and 5,852,244 which are assigned to the same assigns as the present application, the entire disclosure of which is incorporated herein by reference. In a further alternate embodiment, inert sapphire pressure transducers are positioned within respective cavities and in direct contact with the fluid flow, thereby eliminating the isolation membrane.
In use, the fluid control module is coupled in line to a fluid flow circuit. The pressure sensors may be pre-calibrated or the sensors may be calibrated at the time of interconnection with the fluid flow circuit. When calibrating the pressure sensors, the valve may be actuated between an open and closed position. When the pressure sensors indicate that flow has stopped, the output required to actuate the valve may be noted and thereby define an approximation of the closed position of the valve. Various set points may be identified to identify the valve position at various pressures, temperatures and flow rates. The calibration of a single pressure sensor will be described below in greater detail.
Once the flow meter is calibrated, the user may then select whether to control pressure, flow or volume within the fluid flow circuit. If pressure is controlled, the pressure and/or rate of flow is monitored and the valve is accordingly adjusted until a desired set point is reached. If flow is controlled, the pressure and/or flow is monitored and the valve is actuated until the desired set point is reached. The volume of fluid flowing through the fluid conduit may be controlled by monitoring both the pressure and rate of flow and accordingly adjusting the control valve to produce the desired volume of fluid flow. For example, the user may determine that 2 milliliters of fluid is desired. The valve is opened and the pressure and flow rates are monitored, such that it may be determined when 2 milliliters of fluid have passed through the module, wherein the control valve then closes terminating the fluid flow.
When flow is controlled, the controller may store in memory the output of the control valve driver required to obtain a certain flow. In this manner, when the user selects a desired flow, the controller sets the output of the driver approximately equal to an output that previously resulted in the desired flow rate (the macro adjust). Then controller may then manipulate or xe2x80x9cfine tunexe2x80x9d the control valve to precisely obtain the desired flow rate (the micro adjust). When the flow through the module is terminated by closing the control valve, the controller may then automatically adjust or re-zero the pressure sensors such that the difference between the measured pressures of the two pressure sensors is zero. In this manner, inaccuracy due to thermal changes and sensor drift is avoided. In an alternate preferred embodiment, a second valve is provided, wherein the second valve is a dedicated open/close valve. The output of the controller or electronic circuit may be delivered to an external controller or display.